The proposed research will characterize pharmacologically the anticonvulsant activity mediated by a discrete brainstem site, the nucleus reticularis pontis oralis (RPO). Evidence is presented that focal microinfusion of the strychnine-insensitive glycine site partial agonist, D-cycloserine, into the RPO inhibits the tonic hindlimb extension component of maximal electroshock seizures (MES) in rats. Because the anticonvulsant activity induced by RPO microinfusions of D- cycloserine is dose-related, stereospecific and antagonized by 7- chlorokynurenic acid, it is hypothesized that the anticonvulsant activity mediated by the RPO is regulated in part by the strychnine-insensitive glycine site and possibly other receptors known to influence the MES response. The proposed experiment will define the role of the N-methyl-D-aspartic acid (NMDA) receptor/ionophore complex and the associated strychnine- insensitive glycine site within the RPO in the regulation of tonic hindlimb extension. RPO microinfusion of other strychnine-insensitive glycine site partial agonists ((+)HA-966, ACPC) will be tested in MES to determine if the anticonvulsant activity is common to all partial agonists. Agonists (glycine, D-serine) and antagonists (5,7- dichlorokynurenic acid) of the strychnine-insensitive glycine site will be microfused into the RPO to determine if the anticonvulsant effect is mediated by antagonist activity at strychnine-insensitive glycine sites within the RPO. Agonists (NMDA), competitive antagonists (CPP, AP7), and noncompetitive antagonists (MK-801, PCP) of the NMDA receptor will be microfused to further verify the hypothesized RPO NMDA mechanism. To test for other neurotransmitter systems that may mediate anticonvulsant activity in the RPO, microinfusions of GABAergic, cholinergic and noradrenergic agents will also be tested. This includes GABA agonists (muscimol, baclofon) and antagonists (bicuculline, 2-hydroxysaclofen); cholinergic agonist (carbachol) and antagonist (atropine); noradrenergic agonists (corynanthine, clonidine, isoproternol) and antagonists (prazosin, yohimbine, propranolol). The results will identify the RPO as a specific and novel site of anticonvulsant drug action and will delineate specific NMDA receptor and strychnine-insensitive glycine site mechanisms as well as GABAergic, cholinergic and noradrenergic mechanisms within the RPO that mediate the observed anticonvulsant activity in MES. This will enhance the understanding of the basic mechanisms of epilepsy and may provide an improved pharmacological treatment.